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Optics-Lasers - Patricia Bath

STEM Topic 22: Vocabulary

Aspiration: Suction of liquid and debris from the eye during surgery.

Cataracts: Cloudy blemishes that develop in the lens of the eye, causing vision problems.

Cornea: The clear front "window" of the eye that allows light to enter.

Crystalline lens: A clear and flexible structure in the eye that focuses light rays onto the retina.

Excimer: A short-lived molecule used in laser technology, consisting of a noble gas and a reactive gas.

Femtosecond laser-assisted cataract surgery (FLACS): A type of cataract surgery that involves using a laser to create incisions and soften the cataract.

Incision: A small cut or opening made during surgery.

Iris: The colored part of the eye that surrounds the pupil and can change its size to control the amount of light entering the eye.

Irrigation: Supplying liquid to the eye during surgery.

Laserphaco Probe: A device used in cataract surgery that incorporates laser technology to remove cataracts.

LASIK: A type of eye surgery that employs a laser to reshape the cornea and correct vision.

Optic nerve: The nerve that carries visual information from the retina to the brain.

Phacoblates: The process of vaporizing the cataract and lens matter using laser energy.

Phacoblates: The process of vaporizing the cataract and lens matter using laser energy.

Phacoemulsification: A surgical technique that utilizes ultrasound waves to break up and remove a cataract.

Pupil: The black spot in the center of the eye through which light enters.

Refractive power: The ability of the cornea to bend light rays.

Retina: The part of the eye that receives the focused image and sends it as electrical impulses to the brain.

Retina: The part of the eye that receives the focused image and sends it to the brain as electrical impulses.

Ultraviolet range: A range of light wavelengths that are shorter than those visible to the human eye, usually associated with ultraviolet light.


Light rays enter the eye through the cornea, the clear front “window” of the eye. The cornea’s refractive power bends the light rays in such a way that they pass freely through the pupil (the black spot in the center) the opening in the center of the iris through which light enters the eye.

The iris (the colored part of the eye) has the ability to enlarge and shrink, depending on how much light is entering the eye.


After passing through the iris, the light rays pass thru the eye’s natural crystalline lens. This clear, flexible structure works like the lens in a camera to focus the light rays properly. Sometimes and especially as the eye ages, this doesn’t work perfectly.  In many of these situations, the vision can be sharpened through the use of eye glasses.

In a normal eye, the light rays come to a sharp focusing point on the retina. The retina functions much like the film in a camera. It is responsible for capturing all of the light rays, processing them into light impulses through millions of tiny nerve endings, and then sending these light impulses through over a million nerve fibers to the optic nerve.

In summary, the cornea is the clear, transparent front covering which admits light and begins the refractive process. It also keeps foreign particles from entering the eye.


The pupil is an adjustable opening that controls the intensity of light permitted to strike the lens.

The retina receives the image that the cornea focuses through the eye’s internal lens and transforms this image into electrical impulses that are carried by the optic nerve to the brain.




Cataracts are cloudy blemishes that form in the lens of a person’s eye, and they are most commonly seen in people over the age of sixty. 

The Laserphaco Probe

Patricia Bath’s Laserphaco Probe improved on the surgery that was used to remove cataracts.

The probe “consists of an optical laser fiber surrounded by irrigation and aspiration (suction) tubes. The excimer laser probe can be inserted in a tiny (1 mm) incision in the eye. The laser energy phacoblates (vaporizers) the cataract and lens matter within a few minutes. The decomposing lens is extracted when liquid supplied by the irrigation (water) line washes through and is sucked out through the aspiration (suction) tube, and a replacement lens is inserted.”

Developed by Dr. Patricia Bath in 1986, the Laserphaco Probe was one of the first devices to use laser technology for cataract surgery. It paved the way for further development of laser-based cataract surgery techniques.

The Laserphaco Probe has several advantages over traditional cataract surgery techniques. For one, it allows for smaller incisions, which can lead to faster healing times and reduced risk of complications. Additionally, the Laserphaco can be used to break up cataracts that are too hard to remove using manual techniques.

During phacoemulsification, the Laserphaco Probe is used to break up the cloudy lens of the eye into small pieces using ultrasound waves, which are then removed from the eye through a small incision.

Over the years, there have been advancements and improvements made to the technology. Currently, there are several different types of laser-based cataract surgery procedures, including femtosecond laser-assisted cataract surgery (FLACS), which uses a laser to create incisions and soften the cataract, and phacoemulsification with a laser, which combines the laser technology with the use of an ultrasonic probe to break up and remove the cataract.

NOTE: While LASIK and phacoemulsification are both types of eye surgery, they involve different techniques and equipment. In LASIK, a laser is used to reshape the cornea of the eye, while in phacoemulsification; the Laserphaco Probe is used to remove a cloudy lens from the eye.



An excimer laser typically uses a combination of a noble gas (argon (AR), krypton (KR), or xenon (XE) and a reactive gas (fluorine (F) or chlorine (Cl)). Under the appropriate conditions of electrical stimulation and high pressure, a pseudo-molecule (excimer) is fleetingly created, and gives rise to laser light in the ultraviolet range as it decomposes.


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STEM Topic 22: Problem Set
  1. If the human eye blinks 20 times per minute, how many times does it blink in 24 hours?

  2. If a person's pupil has a diameter of 5 mm in bright light and 7 mm in dim light, what is the percentage change in diameter?           

  3. If the retina of the human eye contains about 120 million rods and 6 million cones, what is the ratio of rods to cones?      

  4. If a person's eyes move at an average speed of 500 degrees per second during rapid eye movements (REM) sleep, how many degrees do they move in one minute?

  5. If the average human eye blinks 15 times per minute, how many times will it blink in an hour?

  6. The human eye has a diameter of approximately 2.5 cm. What is the circumference of the human eye?  

  7. If the human eye can distinguish between about 10 million colors, and the visible spectrum of light contains wavelengths from approximately 380 to 740 nanometers, how many colors can the human eye distinguish per nanometer of wavelength?

  8. The human eye is capable of perceiving objects as far away as 20 feet. If a person with 20/20 vision can see an object at 200 feet, what is the magnification factor of the human eye?

  9. If the average human eye has a resolution of 576 megapixels, and a typical high-end digital camera has a resolution of 50 megapixels, how many times more detailed is the human eye compared to the camera?

  10. The human eye can detect light as dim as 0.00001 lux. If a typical candle emits 1 candela of luminous intensity, how far away would the candle need to be from the eye in order to be just barely visible?

  11. The human eye has a natural field of view of approximately 120 degrees horizontally and 90 degrees vertically. What is the total area of the visual field of the human eye in square degrees?

  12. If the human eye has an average speed of saccadic eye movements (the quick, jerky movements the eye makes to change focus) of approximately 90 degrees per second, how long would it take for the eye to make a full rotation?

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